1. Field of the Invention
The present invention relates to an apparatus for detecting a state the wheels are attached to which positions of a vehicle and a method of manufacturing the detecting apparatus.
2. Description of the Related Art
Conventionally, a direct type of apparatus for detecting the inflation pressure of tires of a vehicle has been known. In this type of tire inflation pressure detecting apparatus, there is provided a transmitter with a sensor such as a pressure sensor, which is directly attached to a wheel with a tire. On the side of the vehicle body, an antenna and a receiver are provided. Thus, when the receiver receives, via the antenna, from the transmitter a detection signal detected by the sensor, the receiver is able to detect the inflation pressure of each tire on the received detection signal.
In this direct type of tire inflation pressure detecting apparatus, it is determined whether or not data which has been received is coming from the transmitter of the own vehicle and it is determined by the transmitter that the detection signal is coming from which sensor. For those determinations, as shown in U.S. Pat. No. 5,602,524 (which corresponds to Japanese Patent No. 3212311), data to be transmitted from the transmitter additionally contains ID (identification) information to distinguish the own vehicle from other vehicles and identify a wheel with the transmitter. The ID information is previously stored in the receiver and, when the receiver receives data from the transmitter, the stored ID information and received ID information are used to determine that which wheel the data is coming from.
However, in cases where the user changes the positions of the wheels in, for example, rotating tires, there occurs a problem. That is, the user should read ID information about rotated tires, and update already stored information by the read-out ID information in the receiver. Unless such an information update work is done, the tire inflation pressure detecting apparatus cannot cope with the positional changes of the wheels.
The registration of the ID information in the receiver is a time-consuming task, and thus it is desired to detect the locations of the transmitters (or the associated tires), in other words, to automatically identify the wheel on which each of the transmitters (or the associated tires) is located, even if there is noise in the vehicle.